Phase-locked loops (PLL) find widespread use in frequency synthesizers, clock recovery circuits, phase modulators, and frequency demodulators. Generally, a PLL consists of a voltage-controlled oscillator (VCO), counter, phase/frequency detector (P/FD), charge pump (CP), and RC integration filter.
The phase-locked loop relies on feedback to drive the frequency difference and phase offset between a reference signal and the output of the counter towards zero. Its operation depends on the circuits that comprise the system; and as such, variations in circuit parameters alter the response of the system, lower the stability of the feedback loop, and introduce distortion. The charge pump and integration filter are circuits that are especially sensitive.
It is therefore desirable to improve the performance of the charge pump so that the PLL can better adapt to parameter changes.